歧口凹陷位于黄骅坳陷中北部。沙河街组一段主要成岩作用类型有压实作用、胶结作用、溶蚀作用和交代作用。深度浅于2 200 m 时，溶蚀作用为改善储层物性起到关键作用。沙一段纵向上存在2 个次生孔隙发育带，深度分别在2 700～3 200 m 和3 500～4 200 m 处，孔隙度分布峰值分别在3 150 m 和3 650 m 处。根据镜质体反射率Ro 和粘土矿物混层比及古地温等数据，可将歧口凹陷沙一段的成岩阶段 划分为早成岩A 期、早成岩B 期、中成岩A1 亚期和中成岩A2 亚期，目前该段多处于中成岩阶段A1 到中成岩阶段A2 亚期。

Compaction, cementation, denudation and replacement are the main diagenesis types in the first member of Shahejie Formation in Qikou Sag. Denudation takes a significant part of improving the reservoir property when above 2 200 m. There are two secondary porosity zones developed in the vertical direction, with the depth respectively ranging from 2 700 m to 3 200 m and from 3 500 m to 4 200 m, and the peak value of porosity is at 3 150 m and 3 650 m respectively. Based on the data of vitrinite reflectance, ratio of clay mineral mixed layer and palaeogeothermal, the diagenetic stages of the first member of Shahejie Formation in Qikou Sag can be divided into 4 stages: early diagenesis A stage, early diagenesis B stage, middle diagenesis A1 substage and middle diagenesis A2 substage, and nowit is mainly in the middle diagenesis A1 substage tomiddle diagenesis A2 substage.